Ketenes reaction with, phosgene

Notes. (I) Keten is a poisonous gas having a toxicity comparable with phosgene leaks from the apparatus, which must be contained in a fume cupboard, are recognised by a pungent odour resembling acetic anhydride. For this reason it is customary to attach a second receiver flask containing a compound which readily reacts with keten, e.g. aniline, to the other arm of the three-way stopcock. In this way when the reaction in the main flask is complete the keten gas may be diverted to the second receiver flask while the apparatus is switched off and allowed to cool. Escape to the atmosphere of keten is thereby avoided. 

Attempts to react unsubstituted ketene, CH2=C=0, with phosgene were not successful [175a]. However, a product of the reaction of COCl with an excess of ketene has been claimed to have been prepared in situ, and its reaction product with ethanol has been isolated [293,956,1273] ... 

Oxalyl chloride (ethanedioyl dichioride) can be an effective, alternative, chloroformylating agent to phosgene. The reaction of oxalyl chloride with diphenyl ketene, for example, proceeds under milder conditions than with phosgene to give the identical organic product [1938] ... 

Reactions. As with other tertiary alcohols, esterification with carboxylic acids is difficult and esters are prepared with anhydrides (181), acid chlorides (182), or ketene (183). Ca.rba.mic esters may be prepared by treatment with an isocyanate (184) or with phosgene followed by ammonia or an amine (185). 

Chloroacetyl chloride is manufactured by reaction of chloroacetic acid with chlorinating agents such as phosphoms oxychloride, phosphoms trichloride, sulfuryl chloride, or phosgene (42—44). Various catalysts have been used to promote the reaction. Chloroacetyl chloride is also produced by chlorination of acetyl chloride (45—47), the oxidation of 1,1-dichloroethene (48,49), and the addition of chlorine to ketene (50,51). Dichloroacetyl and trichloroacetyl chloride are produced by oxidation of trichloroethylene or tetrachloroethylene, respectively. 

Homophthalic anhydrides can be prepared by the dehydration of homoph-thalic acid with add chloride, acid anhydride, phosgene, thionyl chloride, benzene sulfonyl chloride, ketene, phosphorous pentoxide, dicyclohexyl-carbodiimide, or J -carbonyldiimidazole. However, these methods are not always effective for the acid-sensitive and/or unreactive homophthaUc acid derivatives. We developed a very mild and efficient method for obtaining homophthaUc anhydrides using (trimethylsilyl)ethoxyacetylene [9] (Scheme 1). Thus the treatment of homophthaUc acid 1 with (trimethylsi-lyl)ethoxyacetylene 2 in inert solvents such as methylene chloride, 1,2-di-chloroethane, and acetonitrile gave the homophthaUc anhydride 3 in a quantitative yield accompanied by ethyl trimethylsilyl acetate as the only side product. The high purity homophthaUc anhydride 3 could be obtained for the next cycloaddition reaction just by evaporation to remove the reaction solvent and the formed ethyl trimethylsilyl acetate. The method is quite useful, and was also applicable to the syntheses of hetero-homophthalic anhydrides 4. 

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